1. Field of the Invention
This invention relates to a cathode for use in electrolysis of an aqueous solution and a method for the production thereof. More specifically, it relates to a cathode for use in electrolysis having a low hydrogen evolution potential and sufficient durability suitable for electrolysis of an aqueous solution of an alkali metal halide and to a method for the production thereof.
2. Description of the Prior Art
In recent years, the role of cathodes for use in the electrolysis industry for producing hydrogen, sodium hydroxide, chlorine, sodium chlorate, sodium hypochlorite, etc., by electrolyzing an aqueous solution, such as an aqueous solution of sodium chloride, has been considered to be important as in the case of anodes.
Heretofore, plates, screens or perforated plates of iron or mild steel have been frequently used as cathodes of this kind for use in electrolysis. Iron as a cathodic material has a considerably low hydrogen evolution potential, but various suggestions have been made in recent years to improve the cathodic material. In the present state-of-the-art where the technique of electrolyzing sodium chloride by an ion-exchange membrane method is being employed and in view of the need for saving energy, cathodes having low hydrogen evolution potentials and good durability have been desired so as to lower the electrolysis voltage further.
Various attempts have been made to reduce the hydrogen evolution potential by developing activated cathodes obtained by coating a cathode substrate with various activating materials.
For example, use of means for increasing the surface area of the cathode is described in, e.g., Japanese Patent Publication No. 6611/56 and Japanese Patent Application (OPI) No. 54877/76 which discloses the provision of a microporous coating of Ni on an iron substrate by coating Ni-Zn on the substrate by plating and then leaching out the Zn.
Coating of an alloy such as Ni-Mo [e.g., as disclosed in British Pat. No. 992,350 (corresponding to Japanese Patent Publication No. 9130/65)] and coating of a platinum-group metal, a platinum-group metal oxide or a mixture thereof with another metal oxide (e.g., as disclosed in Japanese Patent Applications (OPI) Nos. 131474/76 and 11178/77) are also known.
These prior methods have not proved to be fully satisfactory. In the method of forming the microporous coating on the substrate, difficulty is encountered with the leaching out of the Zn as a sacrificing metal. Furthermore, since fine pinholes are formed in the coating, the cathode substrate is exposed to the electrolytic solution and the electrode tends to be damaged by corrosion. The coating of an alloy of an iron-type metal and Mo does not fully reduce the hydrogen evolution potential. A cathode have a coating of a platinum-group metal or an oxide thereof exhibits a low hydrogen evolution potential, but the starting materials are expensive. Moreover, the corrosion resistant coating is not entirely satisfactory. In particular, these cathodes have not proved to be completely satisfactory for use in the electrolysis of sodium chloride using an ion-exchange membrane method in which the cathode is exposed to a high-concentration sodium hydroxide solution at a high temperature.